Epoxy resins based on tetraglycidyl diamines

ABSTRACT

Novel 3-ring tetraglycidates having the formula    &lt;IMAGE&gt;  (I) wherein   &lt;IMAGE&gt;  Y=halogen, C1-C4 alkyl; and n=0 to 4, are disclosed. Epoxy resin systems exhibiting good tensile properties and moisture sensitivity can be made by copolymerizing the tetraglycidates with a polyamine curing agent. Prepregs can be made by combining the epoxy resin systems with a fiber reinforcement. The epoxy resin system may include a co-epoxide.

This is a continuation of application Ser. No. 022,653, filed 3/6/87,abandoned which is a divisional of Ser. No. 853,052, filed 04/17/86 nowU.S. Pat. No. 4,680,341.

FIELD OF THE INVENTION

This invention relates to novel 3-ring tetraglycidates, to epoxy resinsystems made from the novel tetraglycidates, to prepregs made using theepoxy resin systems, and to articles of manufacture which incorporatethe epoxy resins or the prepregs.

BACKGROUND OF THE INVENTION

Polyglycidates (also referred to herein as epoxy compounds) generallyconstitute a class of compounds having at least two glycidyl groups, thereactive moiety in each glycidyl group being the epoxy group.

Many epoxy compounds are commercially available for use in epoxy resinsystems including 2-ring structures such asN,N,N',N',-tetraglycidyl-4,4'-methylene dianiline, having the structure##STR3## This material is made by reacting an excess of epichlorohydrinwith methylene dianiline. It is available commercially as MY-720 fromCiba Geigy Corp., Ardsley, N.Y. and consists of about 70% by weight ofthe above tetraglycidate, the remainder being oligomers andtriglycidates.

Another commonly used 2-ring epoxy compound is made by reactingbisphenol A with epichlorohydrin. Commercially available resins madefrom this reaction contain the structure ##STR4## and include DER 331from Dow Chemical and EPON® 828 (registered trademark) from Shell.

Epoxy groups are reactive to amine and hydroxyl functionalities and canthus be copolymerized (i.e. cured) with compounds containing suchfunctionalities to make epoxy resin systems. Generally polyamines arefavored as curing agents although polyhydroxy curing agents are alsowell known. The epoxy compounds can be reacted with one or more curingagents such that they are crosslinked, thereby finding use as structuraladhesives or as encapsulating materials for electronic components.

Epoxy resin systems are often used in prepregs, ready-to-mold materialscomprising fibrous reinforcement impregnated with uncured or partiallycured epoxy resin systems. Prepregs can be assembled into a final part(such as an airplane wing) and fully cured (C-staged) to form a finishedproduct. Such prepregs find wide use in the aircraft and aerospaceindustries.

Key properties of epoxy resin systems are tensile properties andmoisture sensitivity. High tensile strength is desirable in, forexample, structural adhesives. Low moisture sensitivity is alsodesirable since it leads to improved performance under hot/wetconditions.

Most advanced composites are fabricated from prepreg. Resin systemscontaining an epoxy compound such as MY-720 and aromatic amine hardenerare often used in prepreg since they possess the balance of propertiesrequired for this material. State-of-the-art epoxy/carbon fibercomposites have high compressive strengths, good fatiguecharacteristics, and low shrinkage during cure. However, since mostepoxy formulations used in prepreg are brittle, these composites havepoor impact resistance. In addition, epoxy formulations absorb moisturewhich reduces their high temperature properties and affects theirdimensional stability.

Thus, new epoxy compounds which could be used to make epoxy resinsystems which improve such desirable physical and mechanical properties,relative to present state-of-the-art epoxy systems, would be a usefuladdition to the structural adhesive, airplane, aerospace, and other likeart areas.

THE INVENTION

The present invention provides, in one aspect, novel tetraglycidates ofthe formula ##STR5## wherein ##STR6## Y=halogen, C₁ -C₄ alkyl; and n=0to 4.

Preferred tetraglycidates of the present invention include: ##STR7## Inanother aspect, the invention provides novel epoxy resin systemscomprising a tetraglycidate having the above formula (I) copolymerizedwith a polyamine curing agent (also referred to herein as a hardener).The polyamine hardener may, for example, be any of the well knownaliphatic polyamines such as diethylene triamine, triethylenetetraamine, or tetraethylene pentaamine. Additional hardeners are thosecontaining benzenoid unsaturation such as m- and p-phenylenediamine,1,6-diaminonaphthalene, 4,4'-diaminodiphenyl methane (also known as4,4'-methylene dianiline), 4,4'-diaminodiphenyl ether, sulfanilamide,3methyl-4-aminobenzamide, and 4,4'-diaminodiphenyl sulfone (DDS),4,4'-diaminodiphenyl, ring-alkylated derivatives of m-phenylene diaminesuch as ETHACURE® 100 from Ethyl Corp., Baton Rouge, LA, and the like.Another useful class of polyamine curing agents are those disclosed inU.S. Pat. No. 4,521,583, which have the formula ##STR8## wherein a is 2or 3, R³ is hydrogen, alkyl of 1 to 8 carbon atoms or aryl of 6 to 18carbon atoms, and X is a divalent or trivalent organic hydrocarbon,hetero-interrupted hydrocarbon, or substituted hydrocarbon radical or##STR9## These hardening agents may be prepared from correspondingstarting materials, e.g., nitro compounds, by reduction, for example,according to methods described in U.K. Pat. No. 1,182,377. Particularlycontemplated are those compounds (IX) wherein R³ is hydrogen or C₁ -C₃alkyl and X is a divalent or trivalent radical selected from

(1) divalent groups consisting of --(CH₂)_(y) -- wherein y is an integerof from 2 to 12, ##STR10##

(2) trivalent groups of the formula ##STR11## wherein n and m are thesame or different integers from 1 to 4.

Preferred curing agents are (i) DDS, (ii) those diamines having theformula ##STR12## wherein each of the two amino groups is meta or parato the carbonyl group bonded to the same ring and wherein Y is

    --(CH.sub.2).sub.q --

wherein q is an integer from 2 to 12, preferably 2 to 6, and mostpreferably 3; ##STR13## wherein t is an integer of from 0 to about 5;and ##STR14##

The polyamine curing agent and epoxy compound are mixed essentially inan amount which provides about 0.3 to about 2.0, preferably about 0.4 to1.7, and most preferably about 0.45 to about 1.3 moles of amine hydrogenfor each mole of epoxy groups. The epoxy resin system comprising thecuring agent and epoxy compound may be cured by heating between about200°-400° F. for time periods ranging between about 0.5 and about 12hours.

In another aspect, this invention provides prepregs comprising the novelepoxy resins described herein. Prepregs contain structural fibers. Thestructural fibers which are useful in this invention include carbon,graphite, glass, silicon carbide, poly(benzothiazole),poly(benzimidazole), poly(benzoxazole), alumina, titania, boron, andaromatic polyamide fibers. These fibers are characterized by a tensilestrength of greater than 100,000 psi, a tensile modulus of greater thantwo million psi, and a decomposition temperature of greater than 200° C.The fibers may be used in the form of continuous tows (500 to 400,000filaments each), woven cloth, whiskers, chopped fiber or random mat. Thepreferred fibers are carbon and graphite fibers, aromatic polyamidefibers, such as Kevlar 49 fiber (obtained from E. I. duPont de Nemours,Inc., Wilmington, DE), and silicon carbide fibers.

The epoxy resin in this invention is prepared by standard methods, suchas that described in U.S. Pat. No. 2,951,822 and also in an article byW. T. Hodges et al., SAMPE Quarterly, October 1985, pages 21-25, both ofwhich are incorporated herein by reference. The method entails reactingan aromatic diamine with a four to twenty molar excess ofepichlorohydrin at elevated temperature, generally 50° to 100° C. Thisis followed by dehydrochlorination of the intermediate chlorohydrinamine with aqueous base. The product is then isolated by diluting with awater immiscible solvent, washing with water, drying with a suitabledesiccant, and concentrating to obtain a resinous product. The epoxidethus obtained generally is found by titration to contain 70 to 90% ofthe theoretical amount of epoxy groups. This is due to formation ofoligomeric residues and/or incomplete reaction of the monomeric diaminewith epichlorohydrin. For example, Kirk-Othmer Encyclopedia of ChemicalTechnology, 3rd edition, Volume 9, page 277, gives the epoxy equivalentweight (EEW) of MY-720 (a commonly used commercial glycidyl amine) as117-133. The theoretical EEW is 105. The materials are furthercharacterized by liquid chromatography, infrared spectroscopy, andnuclear magnetic resonance.

The diamines used to form the tetraglycidates of this invention may beprepared by one or more methods disclosed in the literature. Forexample, one general route for preparing the diamines involves thereaction of alpha,alpha'dihydroxy-para-diisopropylbenzene with anilinein the presence of an acidic alumina catalyst and heating the mixture to160°-220° C. to givealpha,alpha'-bis(4-aminophenyl)-para-diisopropylbenzene. Details of themethod are reported by H. J. Buysch et al. in German Offen. DE No.2,111,194 published Sept. 14, l972. A similar method is also disclosedfor the preparation of substituted aminoaryl compounds and derivativesin Netherlands patent application No. 6,408,539 of Jan. 20, 1965 byAllied Chemical Corp.

Another general method which can also be employed for the preparation ofthe diamine starting materials involves the reaction of adiisopropenylbenzene with an aniline hydrochloride under a nitrogenatmosphere and at temperatures of from 180°-200° C. as disclosed in U.S.Pat. No. 3,206,152 assigned to Farbenfabriken Bayer, A.G. A furthermethod for preparing the diamines starting from diisopropenylbenzene isdisclosed in U.S. Pat. No. 3,365,347 which issued Jan. 23, 1968 toAllied Chemical Corp.

Certain of the diamine hardeners are available commercially, such as forexample, alpha,alpha'-bis(4-aminophenyl)-meta-diisopropylbenzene andalpha,alpha'-bis(4-aminophenyl)-para-diisopropylbenzene which can beobtained from Mitsui Petrochemicals Industries Ltd., Japan having anoffice at 200 Park Avenue, New York, N.Y. 10017. Additionally, thediamine hardeners 1,3-bis(4-aminophenyl)benzene and1,3-bis(3-aminophenoxy)benzene are available from Wakayama Seika, Japan.The preparation of other aromatic diamines are described in U.S. Pat.No. 4,222,962 which issued Sept. 16, 1980 to J. P. Pellegrini, Jr.

Epoxy resin systems, i.e., epoxy resin plus hardener, are prepared byheating and stirring the epoxy resin to 60° to 120° C. and adding thehardener. If the hardener is a solid, it is preferably added as a finepowder. An inert diluent such as N,N-dimethyl formamide orN-methylpyrrolidone may be used if desired. Reaction of the epoxy andhardener occur as the mixture is heated. For prepreg, the mixture isB-staged or partially reacted (i.e. typically 3 to 15 percent of theepoxy groups are reacted) in order to obtain a resin system with therequired physical properties (i.e. viscosity and tack).

Prepregs according to the present invention can be made by embeddingfilaments or fibers into, or by coating woven or non-woven webs,rovings, tows, or the like, with a curable epoxy resin resin matrixwhich is ultimately manipulated and cured to a solid composite.Particular selection of the filament, fiber, or textile material, epoxycompound, and curing agent can give a range of curable composites whichcan be tailored to suit a given need or application.

It is preferred to apply the resin as a hot melt to the fiberreinforcement. The B-staged epoxy resin system may conveniently first beapplied to long sheets of differential release paper, i.e. paper towhich a release agent such as any of several of the siliconeformulations well known in the art, has been applied. In a prepregmachine, resin coated on the release paper is transferred to a web offiber. This is done by sandwiching the web between plies of coatedrelease paper and passing the material through a set of heated rollers.The resulting prepreg is then cooled and taken up on a spool. The totalamount of resin applied to the fiber reinforcement is preferably betweenabout 20 and about 50 wt. percent of resin solids based on the weight ofthe uncured composite. If desired, the prepreg may at this point becooled to 0° F. or less by exposure to any convenient cryogenic material(such as dry ice) for shipping or storage.

Upon rewarming to about room temperature, the prepreg can then be usedto make structural parts such as airplane wings or fuselage components.The prepreg may also be used to make other useful articles such as golfshafts, tennis rackets, musical instruments, satellite components, androcket motors. To make useful articles from prepreg, the prepreg may becut into strips and then laid up (e.g. on a mold surface) to create thedesired shape. The shaped, layered composite is then fully cured atpressures between about atmospheric to about 500 psi and temperaturesbetween about 100° C. to about 300° C. in an oven, autoclave, or heatedpressure mold. Depending on the exact epoxy formulation, temperature,and pressure, curing times may range between about 0.2 and about 8hours, the optimum time, pressure, and temperature being easilyascertainable by means of trial runs. This final cure essentiallyC-stages the composite, meaning that the resin has substantially reachedthe final stage of polymerization where crosslinking becomes general andthe composite is substantially infusible.

When making the epoxy resin system for use generally or for usespecifically as a prepreg, a modifying thermoplastic polymer, polymerblend, or elastomer may be used to adjust the viscosity of the resin andto desirably enhance processability and mechanical properties,particularly toughness and damage tolerance. The classes of resins whichare broadly useful include poly(aryl ether) resins as disclosed, forexample, in U.S. Pat. Nos. 4,175,175 and 4,108,837 and exemplified bythermoplastic poly(aryl ether sulfones) available commercially under theregistered trademark UDEL® from Union Carbide Corporation,polyetherimides available, for example, under the registered trademarkULTEM® from General Electric, phenoxy resins (of the type commerciallyavailable under the registered trademark UCAR® from Union CarbideCorporation), polyurethanes, butadiene/styrene/acrylonitrileterpolymers, nylons, butadiene/acrylonitrile liquid rubbers such asHYCAR® CTBN from B. F. Goodrich and the like. The amount ofthermoplastic resin employed will generally fall in a range of about 1to about 30 wt.% based on the weight of the epoxy resin system, althoughamounts above or below this range may be desired in certainapplications. Preferred thermoplastic resins include poly(aryl ethersulfones), polyetherimides, phenoxy resins, and butadiene/acrylonitrileliquid rubbers. The thermoplastic resin is generally added to the epoxycompound and mixed therewith prior to addition of the polyamine curingagent. The modifier will often be miscible with the epoxy compound,although it will also often be occluded as a dispersion within the finalcured epoxy resin once the resin is thermoset.

Co-epoxides may also be used in the epoxy resin system. The co-epoxycompounds (or resins), when employed, may be present in an amount up toabout 40 wt.%, preferably up to about 30 wt.%, based on the amount of(cured or uncured) tetraglycidate used.

Co-epoxy compounds which may be used herein contain two or more epoxygroups having the following formula: ##STR15## The epoxy groups can beterminal epoxy groups or internal epoxy groups. The epoxides are of twogeneral types: polyglycidyl compounds or products derived fromepoxidation of dienes or polyenes. Polyglycidyl compounds contain aplurality of 1,2-epoxide groups derived from the reaction of apolyfunctional active hydrogen containing compound with an excess of anepihalohydrin under basic conditions. When the active hydrogen compoundis a polyhydric alcohol or phenol, the resulting epoxide compositioncontains glycidyl ether groups. A preferred group of polyglycidylcompounds are made via condensation reactions with2,2-bis(4-hydroxyphenyl)propane, also known as bisphenol A, and havestructures such as (X), ##STR16## where n has a value from about 0 toabout 15. These epoxides are bisphenol-A epoxy resins. They areavailable commercially under the trade names such as "Epon 828," "Epon1001", and "Epon 1009" from Shell Chemical Co. and as "DER 331", "DER332", and "DER 334" from Dow Chemical Co. The most preferred bisphenol Aepoxy resins have an "n" value between 0 and 10.

Polyepoxides which are polyglycidyl ethers of 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-biphenol,4,4'-dihydroxydiphenyl sulfide, phenolphthalein, resorcinol,4,2'-biphenol, or tris(4-hydroxyphenyl)methane and the like, are usefulin this invention. In addition, EPON 1031 (a tetraglycidyl derivative of1,1,2,2-tetrakis(hydroxyphenyl)ethane from Shell Chemical Company), andApogen 101, (a methylolated bisphenol A resin from Schaefer ChemicalCo.) may also be used. Halogenated polyglycidyl compounds such as D.E.R.542 (a brominated bisphenol A epoxy resin from Dow Chemical Company) arealso useful. Other suitable epoxy resins include polyepoxides preparedfrom polyols such as pentaerythritol, glycerol, butanediol ortrimethylolpropane and an epihalohydrin.

Polyglycidyl derivatives of phenol-formaldehyde novolaks such as XIwhere n=0.1 to 8 and cresol-formaldehyde novalaks such as XII wheren=0.1 to 8 are also useable. ##STR17## The former are commerciallyavailable as D.E.N. 431, D.E.N. 438, and D.E.N. 485 from Dow ChemicalCompany. The latter are available as, for example, ECN 1235, ECN 1273,and ECN 1299 (obtained from Ciba-Geigy Corporation, Ardsley, NY).Epoxidized novolaks made from bisphenol A and formaldehyde such as SU-8(obtained from Celanese Polymer Specialties Company, Louisville, KY) arealso suitable.

Other polyfunctional active hydrogen compounds besides phenols andalcohols may be used to prepare the polyglycidyl adducts useful in thisinvention. They include amines, aminoalcohols and polycarboxylic acids.

Adducts derived from amines include N,N-diglycidyl aniline,N,N-diglycidyl toluidine, N,N,N',N'-tetraglycidyl xylylenediamine,(i.e., XIII) N,N,N',N'-tetraglycidyl-bis(methylamino)cyclohexane (i.e.XIV) , N,N,N',N'-tetraglycidyl-4,4'-methylene dianiline, (i.e. XV)N,N,N,',N'-tetraglycidyl-3,3'-diaminodiphenyl sulfone, andN,N'-dimethyl-N,N'-diglycidyl-4,4'-diaminodiphenyl methane. Commerciallyavailable resins of this type include Glyamine 135 and Glyamine 125(obtained from F.I.C. Corporation, San Francisco, CA.), Araldite MY-720(obtained from Ciba Geigy Corporation) and PGA-X and PGA-C (obtainedfrom The Sherwin-Williams Co., Chicago, Ill.).

Also suitable are modified epoxies such as Tactix 71788, 71794, and71795 epoxy resins (obtained from Dow Chemical Corporation, Midland,MI.). ##STR18##

Suitable polyglycidyl adducts derived from aminoalcohols includeO,N,N-triglycidyl-4-aminophenol, available as Araldite 0500 or Araldite0510 (obtained from Ciba Geigy Corporation) andO,N,N-triglycidyl-3-aminophenol (available as Glyamine 115 from F.I.C.Corporation).

Also suitable for use herein are the glycidyl esters of carboxylicacids. Such glycidyl esters include, for example, diglycidyl phthalate,diglycidyl terephthalate, diglycidyl isophthalate, and diglycidyladipate. There may also be used polyepoxides such as triglycidylcyanurates and isocyanurates, N,N-diglycidyl oxamides, N,N'-diglycidylderivatives of hydantoins such as "XB 2793" (obtained from Ciba GeigyCorporation), diglycidyl esters of cycloaliphatic dicarboxylic acids,and polyglycidyl thioethers of polythiols.

Other epoxy-containing materials are copolymers of acrylic acid estersof glycidol such as glycidyl acrylate and glycidyl methacrylate with oneor more copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidyl methacrylate, 1:1 methyl methacrylate-glycidylacrylate and 62.5:24:13.5 methyl methacrylate:ethyl acrylate:glycidylmethacrylate.

Silicone resins containing epoxy functionality, e.g.,2,4,6,8,10-pentakis[3-(2,3-epoxypropoxy)propyl]-2,4,6,8,10-pentamethylcyclopentasiloxaneand the diglycidyl ether of1,3-bis-(3-hydroxypropyl)tetramethyldisiloxane) are also useable.

The second group of epoxy resins is prepared by epoxidation of dienes orpolyenes. Resins of this type include bis(2,3-epoxycyclopentyl)ether,XVI, ##STR19## copolymers of XVI with ethylene glycol which aredescribed in U.S. Pat. No. 3,398,102,5(6)-glycidyl-2-(1,2-epoxyethyl)bicyclo[2.2.1]heptane, XVII, anddicyclopentadiene diepoxide. Commercial examples of these epoxidesinclude vinylcyclohexene dioxide, e.g., "ERL-4206" (obtained from UnionCarbide Corp.), 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, e.g., "ERL-4221" (obtained from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate, e.g., "ERL-4201" (obtained from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, e.g., "ERL-4289"(obtained from Union Carbide Corp.), dipentene dioxide, e.g.,"ERL-4269"(obtained from Union Carbide Corp.)2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanemetadioxane, e.g.,"ERL-4234" (obtained from Union Carbide Corp.) and epoxidizedpoly-butadiene, e.g., "Oxiron 2001" (obtained from FMC Corp.)

Other suitable cycloaliphatic epoxides include those described in U.S.Pat. Nos. 2,750,395; 2,890,194; and 3,318,822 which are incorporatedherein by reference, and the following: ##STR20##

Other suitable epoxides include: ##STR21## where n is 1 to 4, m is(5-n), and R is H, halogen, or C₁ to C₄ alkyl.

Reactive diluents containing one epoxide group such as t-butylphenylglycidyl ether, may also be used. The reactive diluent may comprise upto 25 percent by weight of the epoxide component.

The preferred co-epoxy resins are bisphenol A epoxy resins of formula Xwhere n is between 0 and 5, epoxidized novolak resins of formula XI andXII where n is between 0 and 3, N,N,N',N'-tetraglycidyl xylylenediamine, and diglycidyl phthalate.

The epoxy resin system may additionally contain an accelerator toincrease the rate of cure. Accelerators which may be used herein includeLewis acid:amine complexes such as BF₃.monoethylamine, BF₃ piperidiene,BF₃.2-methylimidazole; amines, such as imidazole and its derivativessuch as 4-ethyl-2-methylimidazole, 1-methylimidazole, 2-methylimidazole;N,N-dimethylbenzylamine; acid salts of tertiary amines, such as thep-toluenesulfonic acid:imidazole complex, salts of trifluoromethanesulfonic acid, such as FC-520 (obtained from 3M Company),organophosphonium halides, dicyandiamide, 1,1-dimethyl-3-phenyl urea(Fikure 62U from Fike Chemical Co.), and chlorinated derivatives of1,1-dimethyl-3-phenyl urea (monuron and diuron from du Pont). If used,the amount of cure accelerator may be from 0.02 to 10 percent of theweight of the epoxy resin system (i.e., epoxy plus hardener).

In addition to structural fibers, thermoplastic polymers, and cureaccelerators, the epoxy resin systems may also contain particulatefillers such as talc, mica, calcium carbonate, aluminum trihydrate,glass microballoons, phenolic thermospheres, pigments, dyes, and carbonblack. In prepregs, up to half of the weight of structural fiber in thecomposition may be replaced by filler. Thixotropic agents such as fumedsilica may also be used.

In the epoxy resin systems (i.e. epoxy plus hardener) of this invention,the proportion of epoxy resin can be about 95 to about 30 percent byweight, preferably about 80 to about 35 wt. percent, and the proportionof hardener can be from about 5 to about 70 wt. percent, preferablyabout 15 to about 60 wt. percent.

In prepregs and composites (epoxy plus hardener and structural fiber),the percent by weight of the epoxy resin system can be from about 20 to80 percent by weight, based on the weight of the prepreg or composite,preferably about 25 to about 60 wt. percent. The structural fibercomprises 80 to 20 wt. percent, preferably 75 to 40 wt. percent of thetotal composition.

The invention is further disclosed and described by means of thefollowing examples which are not to be taken as limiting.

EXAMPLE 1

This example describes the synthesis of Bisaniline P tetraglycidate (BAPTG) from Bisaniline P (BAP).

BAP (1.2 kg), epichlorohydrin (3.0 kg) ethanol (1.6 l), and 200 ml ofwater were placed into a 5 liter three neck, roundbottom flask that wasequipped with a mechanical stirrer, addition funnel, and a thermometerthat was connected to a Therm-o-watch temperature controller. Themixture was placed under a blanket of nitrogen and heated to reflux withgentle stirring. The reaction mixture was a slurry initially but quicklybecame homogeneous as the reflux temperature was approached. After themixture had refluxed for 4 hours, the temperature was lowered to 60° C.and 1.2 kg of 50% aqueous sodium hydroxide were added at such a ratethat the temperature was maintained at 60° C. When addition wascomplete, the temperature was held at 60° C. for 1 hour, at which timeheating was discontinued. When the mixture was at room temperature, theliquid was decanted from the flask into a separatory funnel. The largemass of sodium chloride left behind was washed with methylene chloride(2×100 ml) and these washings were added to the separatory funnel. Water(200 ml) was added to the separatory funnel and the layers wereseparated. The organic phase was washed with water (2×1 liter), brine(1×1 liter), dried (Na₂ SO₄), filtered, and the filtrate wasconcentrated on a rotary evaporator (50 mm Hg, at 80° C., then 0.1 mm Hgat 80° C.). 1.9 kg (93 %) of a light brown viscous liquid was obtained.Physical Data: Epoxy equivalent weight=160 g/eq.

EXAMPLE 2

This example describes the preparation ofbis-1,4-(4-aminophenoxy)benzene tetraglycidate (TPE-QTG) frombis-1,4-(4-aminophenoxy)benzene (TPE-Q).

Following the procedure of Example 1, 200 g TPE-Q, 465 gepichlorohydrin, 200 ml ethanol, and 30 ml of water produced 310 g (70%)of a viscous liquid having an EEW=170 g/eq.

EXAMPLE 3

This example describes the preparation of 1,3-bis(4-aminophenoxy)benzenetetraglycidate (TPE-RTG) from 1,3-bis(4-aminophenoxy)benzene (TPE-R).

Following the procedure of Example 1, 1.0 kg TPE-R, 3.0 kgepichlorohydrin, 0.6 l ethanol, and 100 ml of water afforded 1.4 kg(82%) of a viscous amber liquid. EEW=174 g/eq.

The following examples describe the preparation of unreinforced castingsof the new tetraglycidates cured with trimethylene glycoldi-p-aminobenzoate (DADE).

Glass transition temperatures were determined on a DuPont 982 thermalanalyzer as the maximum of the loss modulus peak of a DMA scan. Watersensitivity was determined by soaking a 2.0"×0.5"×1/8" coupon in waterfor 2 weeks at 71.1° C. (160° F.). The percent weight gain of the couponwas determined after soak.

EXAMPLE 4

40 g of the epoxy of Example 1 were heated to 100° C. in a three-neck500 ml roundbottom flask fitted with a thermometer connected to aTherm-o-watch temperature controller and a mechanical stirrer. 24.0 g ofDADE were added. After the temperature came back to 100° C., all thediamine dissolved after another 15-45 minutes. Vacuum (50 mm Hg) wasapplied for about 5 minutes, stirring was discontinued and the vacuumwas applied for 5 minutes more. The resin was then poured into a mold(dimensions 8"×10"×1/8") which had been warmed in a 90° C. oven. Thecasting was cured as follows: 75° C. (4 hours)→4 hours→120° C. (2hours)→2 hours→179° C. (2 hours).

EXAMPLE 5

Following the procedure of Example 4, 75 g of TPE-QTG and 45 g of DADEproduced a void free, transparent casting.

EXAMPLE 6

Following the procedure of Example 4, 100 g TPE-RTG and 56 g of DADEproduced a void free transparent casting.

Control A

This example is comparative and describes the preparation ofunreinforced castings from an epoxy resin having the trade designationMY-720 and having as its major constituent a compound of the formula:##STR22##

100 g of MY-720 were placed in a three-neck roundbottom flask equippedwith a mechanical stirrer, thermometer fitted with a Therm-o-watchtemperature controller, and a gas adaptor. The epoxy was warmed to 110°C., at which time 61 g of DADE were added. Heating was continued untilthe DADE was completely dissolved. Vacuum (50 mm Hg) was applied, andafter 5 minutes stirring was stopped, the heating mantle was removed,and the vacuum was continued 5 more minutes. The resin was poured into a8"×10"×1/8" mold that was prewarmed in a 100° C. oven.

Table I lists physical data for the castings of Examples 5-8 and ControlA.

                                      TABLE I                                     __________________________________________________________________________    PROPERTIES OF UNREINFORCED CASTINGS                                                     Example 4                                                                            Example 5                                                                             Example 6                                                                             Control A                                    __________________________________________________________________________    Composition.sup.a                                                                       BAPTG 40 g                                                                           TPE-QTG 75 g                                                                          TPE-RTG 100 g                                                                         MY-720 100 g                                           DADE 24 g                                                                            DADE 45 g                                                                             DADE 56 g                                                                             DADE 61 g                                    Tensile Properties.sup.b                                                      Tensile Strength                                                                        13.0   13.5    15.1    10.5                                         (ksi)                                                                         Tensile Modulus                                                                         482    490     465     404                                          (ksi)                                                                         Elongation (%)                                                                          3.8    4.4     3.4     3.8                                          Tg (°C.) Dry                                                                     175    180     198     210                                          Wet.sup.b 130    135     --      173                                          Water Uptake (%).sup.c                                                                  3.0    3.0     --      3.4                                          __________________________________________________________________________     .sup.a NH/epoxide stoichiometry = 1.0/1.0                                     .sup.b ASTM D638                                                              .sup.c Measured after soaking in water for two weeks at 71.1° C.       (160° F.).                                                        

It is apparent that compositions according to the invention havesuperior tensile strength, tensile modulus, and water resistancecompared to Control A.

EXAMPLE 7

This example describes the preparation of an unreinforced casting ofBAPTG, MY-720, and 4,4-diaminodiphenylsulfone (DDS).

75 g of the epoxy of Example 1 and 75 g of MY-720 were heated to 100° C.in a 3-neck roundbottom flask equipped with a paddle stirrer, and athermometer connected to a Therm-o-watch temperature controller. 33 g ofDDS were slowly added with stirring. After the mixture had been heatedfor 90 minutes at 100° C., the diamine had dissolved. The resin was thendegassed and poured into a mold (8"×10"×1/8"). The casting was cured inthe same manner as Example 4.

                  TABLE II                                                        ______________________________________                                        PROPERTIES OF AN UNREINFORCED CASTING                                                            Example 7.sup.b                                            ______________________________________                                        Composition          BAPTG 75 g                                                                    MY-720 75 g                                                                   DDS 33 g                                                 Tensile Properties.sup.a                                                      Tensile Strength     6.3                                                      (ksi)                                                                         Tensile Modulus      672                                                      (ksi)                                                                         Elongation (%)       1.1                                                      ______________________________________                                         .sup.a ASTM D638                                                              .sup.b NH/epoxide stoichiometry 0.5/1.0                                  

EXAMPLE 8 and Control B

This example describes the preparation of undirectional epoxy/graphiteprepreg.

A thermosetting composition like that of Example 4 was prepared byblending 1219 g of BAP TG (EEW=176) and 510 g of the diamine DADE at100° C. for approximately 90 minutes. At this point, a 1.5 mil film wascast and was determined to have appropriate tack for prepreg. It wascoated on 13.5 inch wide release paper (type 2-60-SF-157 and 168A,obtained from Daubert Coated Products Dixon, IL) at a coating weight of110 g/m².

Twelve-inch wide undirectional prepreg tape was made by forming a ribbonof 78 tows of carbon fiber and contacting it between 2 plies ofepoxy-coated release paper in a prepreg machine. In the prepreg machine,the sandwich of fiber and coated release paper passed over a series ofheated rollers to melt the resin into the fibers. The finished tapecontained about 64 percent by weight of fiber. Its thickness was about0.007 inches. The fiber was a polyacrylonitrile-based fiber with atensile strength of 5.5×10⁵ psi and a tensile modulus of 35×10⁶ psi.

Control B

This example is comparative and describes the preparation ofunidirectional epoxy/graphite prepreg.

A thermosetting composition like that of Control A was prepared byblending 1227 g of MY-720 and 773 g of DADE. The resin was advanced byheating for 100 minutes at 100° C. After the mixture cooled to 70° C.,it was coated on 13.5 inch wide release paper (type 2-60-SF-157 and168A, obtained from Daubert Coated Products Dixon, IL) at a coatingweight of 104 g/m².

Twelve-inch wide undirectional prepreg tape was made by forming a ribbonof 78 tows of carbon fiber and contacting it between 2 plies ofepoxy-coated release paper in a prepreg machine. In the prepreg machine,the sandwich of fiber and coated release paper passed over a series ofheated rollers to melt the resin into the fibers. The finished tapecontained about 70 percent by weight of fiber. Its thickness was about0.007 inches. The fiber was a polyacrylonitrile-based fiber with atensile strength of 5.5×10⁵ psi and a tensile modulus of 35×10⁶ psi.

EXAMPLE 9

Example 9 describes the cured unidirectional laminate made from theprepreg of Example 8. The laminate was cured in an autoclave at 355° F.for 2 hours under a pressure of 90 psi. Seven plies of prepreg were usedto make the specimen. Compressive properties were measured using amodified ASTM-D695 procedure. Unidirectional graphite/epoxy tabs wereadded to prevent the sample ends from crushing. A gauge length ofapproximately 0.188 inches was used. End tabs on compressive sampleswere adhered using FM-300 film adhesive (obtained from American CyanamidCompany, Havre de Grace, MD), which was cured at 177° C. for 1 hour. Thelongitudinal compressive strengths of unidirectional laminates ofExample 9 is shown in Table III.

                  TABLE III                                                       ______________________________________                                         LONGITUDINAL COMPRESSIVE STRENGTH (ksi)                                      CONDITION:                                                                    ROOM                                                                          TEMPERATURE (DRY)                                                                             180° F. (DRY)                                                                      180° F. (WET).sup.a                        ______________________________________                                        231             226         195                                               ______________________________________                                         .sup.a Specimens were soaked in water 2 weeks at 160° F. prior to      testing.                                                                 

For many applications, a longitudinal compressive strength of at least150 ksi is required. The results in Table III indicate that thecompositions of this invention possess excellent compressive strengthseven under hot/wet conditions.

EXAMPLE 10 and Control C

This example demonstrates the compressive strength after impact of aquasiisotropic laminate fabricated with the composition of thisinvention and with a control. The test employed measures the damagetolerance of composites. The latter depends on the choice of matrixresin. Test specimens had dimensions of 6×4×approximately 0.2 inches.The panels were impacted in the center with a Gardner type Impact Tester(Gardner Laboratories, Bethesda, MD) having a 5/8 inch diameterspherical indenter. The impact was normal to the plane of the fibers.When impacted, the laminate was simply supported over a 3 inch by 5 inchcutout in an aluminum plate with a plywood backup. The impacted panelwas tested for residual compressive strength in a steel fixture thatconstrained the edges from out-of-plane buckling. Results are tabulatedin Table IV.

                  TABLE IV                                                        ______________________________________                                        RESIDUAL COMPRESSIVE STRENGTH (in 10.sup.3 psi)                               AFTER IMPACT RESULTS.sup.a                                                    EXAMPLE:       EXAMPLE 10  CONTROL C.sup.b                                    ______________________________________                                        Impact Level: 1500                                                                           24.5        19.3                                               (In lb/in)                                                                    ______________________________________                                         .sup.a Cure schedule: 2 hours at 355° F. Layup:                        [+45/90/-45/0].sub.3s                                                         Autoclave pressure 90 psi                                                     .sup.b Made from the MY720/DADE prepreg of Control B                     

It is clear that the residual compressive strength of laminates madewith the composition of this invention is significantly higher than thatof the control. Thus, the fiber reinforced composites of this inventionhave improved impact resistance.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims.

What is claimed is:
 1. A prepreg, comprising:an epoxy resin systemcomprising a tetraglycidate of the formula ##STR23## wherein ##STR24##Y=halogen, C₁ -C₄ alkyl; and n=0 to 4 a polyamine curing agent; and afiber reinforcement.
 2. A prepreg as defined in claim 1, wherein saidpolyamine is selected from the group consisting of aliphatic polyaminesand polyamines containing benzenoid unsaturation.
 3. A prepreg asdefined in claim 2, wherein said aliphatic polyamine is selected fromthe group consisting of diethylene triamine, triethylene tetraamine, andtetraethylene pentaamine
 4. A prepreg as defined in claim 2, whereinsaid polyamine containing benzenoid unsaturation is selected from thegroup consisting of m-phenylenediamine, p-phenylenediamine,1,6-diaminonaphthalene, 4,4'-diaminodiphenyl methane,4,4'-diaminodiphenyl ether, sulfanilamide, 3-methyl-4-aminobenzamide,4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl, and ring alkylatedderivatives of m-phenylene diamine.
 5. A prepreg as defined in claim 1,wherein said polyamine has the formula ##STR25## wherein: a is 2 or 3;R³is hydrogen, alkyl of 1 to 8 carbon atoms, or aryl, of 6 to 18 carbonatoms; and X is a divalent or trivalent organic hydrocarbon,hetero-interrupted hydrocarbon, substituted hydrocarbon radical, or##STR26##
 6. A prepreg as defined in claim 5,wherein R³ is hydrogen,alkyl of 1 to 3 carbon atoms, or phenyl; and X is a divalent ortrivalent radical selected from (1) divalent groups consisting of--(CH₂)₄ -- wherein y is an integer of from 2 to 12, ##STR27## (2)trivalent groups of the formula ##STR28## and --(CH₂)_(n)--CH--(CH₂)_(m) -- wherein n and m are the same or different integersfrom 1 to
 4. 7. A prepreg as defined in claim 1, wherein said polyamineis selected from the group consisting of (i) 4,4'-diaminodiphenylsulfone, (ii) diamines having the formula ##STR29## wherein each of thetwo amino groups is meta or para to the carbonyl group bonded to thesame ring and wherein Y is

    --(CH.sub.2).sub.q --

wherein q is a integer from 2 to 12, ##STR30## wherein t is an integerof from 0 to about 5, and ##STR31##
 8. A prepreg as defined in claim 7,wherein q is from about 2 to about
 6. 9. A prepreg as defined in claim 8wherein q is
 3. 10. A prepreg as defined in claim 1, wherein saidpolyamine curing agent is mixed with said tetraglycidate in an amountwhich provides about 0.3 to about 2.0 moles of amine hydrogen for eachmole of epoxy groups.
 11. A prepreg as defined in claim 10, wherein saidamount provides about 0.4 to about 1.7 moles of amine hydrogen for eachmole of epoxy groups.
 12. A prepeg as defined in claim 11, wherein saidamount provides about 0.45 to about 1.3 moles of amine hydrogen for eachmole of epoxy groups.
 13. A prepreg as defined in claim 1, wherein saidfiber reinforcement is a material selected from the group consisting ofglass, carbon, graphite, silicon carbide, boron, alumina, titania,poly(benzothiazole), poly(benzimidazole), poly(benzoxazole), andaromatic polyamide fibers.
 14. A prepreg as defined in claim 1, whereinsaid fiber reinforcement is in the form of continuous tows, woven cloth,whiskers, chopped fiber, or random mat.
 15. A prepreg as defined inclaim 1, wherein said epoxy resin system further comprises a co-epoxide.16. A prepreg as defined in claim 15, wherein said co-epoxide is presentin an amount up to about 40 wt. percent based on the total amount oftetraglycidate.
 17. A prepreg as defined in claim 16, wherein saidco-epoxide is present in an amount up to about 30 wt. percent based onthe total amount of tetraglycidate.
 18. A prepreg as defined in claim15, wherein said co-epoxide has the structure ##STR32## where n has avalue from about 0 to about
 15. 19. A prepreg as defined in claim 18,wherein n has a value from about 0 to about
 10. 20. A prepreg as definedin claim 15, wherein said co-epoxide is a polyepoxide which is apolyglycidyl ether.
 21. An epoxy resin system as defined in claim 20,wherein said co-epoxide is a polyepoxide selected from the groupconsisting of polyglycidyl ethers of 4,4'-dihydroxydiphenyl methane,4,4'-dihydroxydiphenyl sulfone, 4,4'-biphenol, 4,4'-dihydroxydiphenylsulfide, phenolphthalein, resorcinol, 4,2'-biphenol, andtris(4-hydroxyphenyl)methane.
 22. A prepreg as defined in claim 15,wherein said co-epoxide is a polyglycidyl derivative of aphenol-formaldehyde novolak or a cresol-formaldehyde novolak.
 23. Aprepreg as defined in claim 22, wherein said phenol-formaldehyde novolakhas the structure XI and said cresol-formaldehyde novolak has thestructure XII ##STR33## where n=0.1 to
 8. 24. A prepreg as defined inclaim 15, wherein said co-epoxide is a polyglycidyl adduct of an amine,an aminoalcohol, or a polycarboxylic acid.
 25. A prepreg as defined inclaim 24, wherein said polyglycidyl adduct of an amine is selected fromthe group consisting of N,N-diglycidyl aniline, N,N-diglycidyltoluidine, N,N,N',N'-tetraglycidylxylylene diamine,N,N,N',N'-tetraglycidyl-bis(methylamino)cyclohexane,N,N,N',N'-tetraglycidyl-4,4'-methylene dianiline,N,N,N',N'-tetraglycidyl-3,3'-diaminodiphenyl sulfone, andN,N'-dimethyl-N,N'-diglycidyl-4,4'-diaminodiphenyl methane.
 26. Aprepreg as defined in claim 24, wherein said polyglycidyl adduct of anaminoalcohol is O,N,N,-triglycidyl-3-aminophenol orO,N,N-triglycidyl-4-aminophenol.
 27. A prepreg as defined in claim 24,wherein said polyglycidyl adduct of a polycarboxylic acid is a glycidylester.
 28. A prepreg as defined in claim 27, wherein said glycidyl esteris selected from the group consisting of diglycidyl phthalate,diglycidyl terephthalate, diglycidyl isophthalate, and diglycidyladipate.
 29. A prepreg as defined in claim 15, wherein said co-epoxideis selected from the group consisting of triglycidyl cyanurates andisocyanurates, N,N-diglycidyl oxamides, N,N'-diglycidyl derivatives ofhydantoins, diglycidyl esters of cycloaliphatic dicarboxylic acids, andpolyglycidyl thioethers of polythiols.
 30. A prepreg as defined in claim15, wherein said co-epoxide is a copolymer of an acrylic acid ester ofglycidol with one or more copolymerizable vinyl compounds.
 31. A prepregas defined in claim 15, wherein said co-epoxide is a silicone resincontaining epoxy functionality.
 32. A prepreg as defined in claim 15,wherein said co-epoxide is an epoxy resin prepared by epoxidation ofdienes or polyenes.
 33. A prepreg as defined in claim 15, wherein saidco-epoxide is cycloaliphatic.
 34. A prepreg as defined in claim 1,further comprising a thermoplastic polymer, polymer blend, or elastomer.